[SPAM]Re: [PATCH v7] scsi: ufs: Quiesce all scsi devices before shutdown

[Bart Van Assche]

On 2020-08-03 20:19, Chaotian Jing wrote:
> I have a question about this:
> thread A is running the shutdown flow, but thread B is still access
> UFS(sda/sdb/sdc..), is it expected ? after the sd_shutdown() completed,
> if thread B still has access to UFS(sda/sdb/sdc...), it will make the
> sd_shutdown() make no sense because the sd_resume() will send ssu to
> start sda/sdb/sdc.
> 
> so can we avoid this and ensure that there is no request to sda after
> sda's shutdown() is completed ?
> 
> so that is it possible to modify the sd_shutdown() ? take "sda" for
> example: after sync cache && ssu to stop sda, do blk_cleanup_queue()
> then it will ensure no runtime resume of sda and no more new requests to
> sda.
> 
> then, for UFSHCI host driver, its shutdown() no need and should not
> handle the sda/sdb/sdc's queue and device status, because these
> devices(sda/sdb/sdc) has already complete its shutdown.
> just like part of Can's comment, UFSHCI's shutdown() should only handle
> hba->sdev_ufs_device.

My understanding is that ufshcd_shutdown() is only called if no
recovery is possible, e.g. from the pci_driver.shutdown callback. Hence
the proposal to call scsi_remove_device() from inside ufshcd_shutdown().
It may be necessary to call scsi_target_unblock(...,
SDEV_TRANSPORT_OFFLINE) first to flush queued I/O. Other contexts that
may submit I/O while ufshcd_shutdown() is in progress, e.g. the sd
driver, are expected to hold a reference on the SCSI device with
scsi_device_get() / scsi_device_put(). I think the sd driver already
does that. In other words, no changes should be necessary in the sd
driver.

Thanks,

Bart.